Scroll-type fluid displacement apparatus are well-known in the prior art. For example, U.S. Pat. No. 801,182 (Creux) discloses the basic construction of a scroll-type fluid displacement apparatus which includes two scroll members, each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that the spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces which define and seal off at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surface, thus changing the volume of fluid pockets. Since the volume of fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll-type fluid displacement apparatus is applicable to compress, expand or pump fluids.
In a conventional refrigerant compressor, a charge of refrigerant fluid and lubricating oil is introduced in to the area of the fluid pockets. The fluid is compressed by the orbital motion of scroll member and the compressed fluid is fed out of the compressor. The lubricating oil splashes up in the interior of the compressor housing to lubricate desired components of the compressor. The splashed lubricating oil mixes with the fluid, and the fluid fills the interior of the compressor housing to thereby lubricate the moving parts of the compressor. However, if only the splashed oil or oil-fluid mixture is used for lubrication, lubrication of the driving mechanism and other components which are located in the center portion of the compressor is insufficient, because the splashed oil and the fluid are forced outwardly by the centrifugal force of the moving parts.
One solution to the above-discussed disadvantage is described in U.S. Pat. No. 4,314,796. In this apparatus, the driving mechanism for the orbiting scroll comprises a drive shaft and a drive pin eccentrically projecting from the inner end surface of the drive shaft. The drive pin is fitted within a boss projecting from the end surface of the circular end plate through a bearing so that the orbiting scroll is driven by the rotation of the drive shaft. In this construction, the bearing disposed on the drive pin is lubricated by the lubricating oil which flows from a shaft seal cavity through a passageway formed in the drive shaft and drive pin. Since the lubricating oil is supplied to the boss portion from the shaft seal cavity by a difference of centrifugal force, the lubrication to the bearing can be insufficient. In order to increase the flow of oil from the shaft seal cavity to the boss portion, the eccentric throw of the drive pin must be increased so that the diameter of the compressor is increased.